There are no completely carbohydrate-free and fat-free sour milk products in the market at this moment. There is a great interest in and a need and demand for extremely low-energy food products, light products and weight-control products.
In the preparation of sour milk products, it is typical that starter is added to homogenized, highly heat-treated milk, which, as it sours the milk, provides it with the structure and taste properties typical of the product. As a result of heating, some of the whey proteins of the milk are denatured.
Publication WO 2004/075644 (HP Hood LLC) describes a reduced carbohydrate microbiologically soured dairy product and a process for manufacturing it. An unflavoured soured milk product contains 2.21 to 3.09% carbohydrates, 3.98 to 4.86% protein and 1.33 to 2.20% fat. A flavoured soured product, in turn, contains 3.10 to 3.97% carbohydrates, 0.44 to 1.32% fat and 3.98 to 4.86% protein.
Publication US 2006/0057247 (Ngyen et al.) relates to a process for producing a microbiologically soured dairy product, which contains a small amount of added carbohydrates, from ultrafiltered milk and to a soured dairy product, which contains less than 4.9% carbohydrates and has a viscosity of 900 to 1 600 mPas and a pH of 4.1 to 4.5.
A problem with the products described in these publications is, however, the fact that they contain a great deal of carbohydrates and are, thus, not low-energy products. The maximum carbohydrate contents given to the products are close to the normal carbohydrate content of milk, that is, approximately 4.9%.
Control of the preparation of microbiologically soured low-energy products and the adjustment and maintenance of conditions, such as pH, temperature and time, is problematic, arduous and difficult to manage. In addition, the organoleptic properties of the products are sensitive to disturbances caused by changes in conditions. The preparation of extremely low-energy soured products, especially those from which carbohydrates are removed, is difficult to do with starters, because starter bacteria do not proliferate and acid does not form without adding sugar. Additional costs then arise from raw materials, for instance. In addition, the preparation process and product are more and more difficult to control when a carbohydrate-free, extremely low-energy product is prepared. It is known in the field to add a cross-linking enzyme to the protein source to minimize structural problems. A problem then arises that the processes and their control are further complicated and become more difficult as more preparation steps are added. Thus, simple product formulations and cost-effective preparation processes are needed to control the problems, such as post-souring and structural problems like a powdery structure, caused by the generally known processes to the products.
In the preparation of sour products, chemical souring with for instance glucono-delta-lactone, lactic acid, hydrochloric acid, citric acid, or a combination of different acids is a known alternative for microbiological souring with starters. For instance Schorsch, C. et al. [Int Dairy J 10 (2000), 519-528] and Myllärinen, P. et al. [Int Dairy J, 17 (2007) 800-807] disclose that milk sours chemically by adding glucono-delta-lactone (GDL), such as bacteria producing lactic acid, depending on the souring conditions. Schorsch, C. et al. describe the preparation of casein gel from ultrafiltered calcium-phosho-caseinate by treating it with a cross-linking enzyme, transglutaminase. In publication Int Dairy J 10 (2000) 529-539 (Schorsch, C. et al.), in turn, casein gel is prepared from ultrafiltered calcium-phosho-caseinate by treating it with a cross-linking enzyme and souring it chemically with glucono-delta-lactone (GDL). Myllärinen, P. et al. describe the preparation of milk protein from sodium caseinate or acid casein by chemical souring with GDL and adding treatment with a cross-linking enzyme to the souring. Menéndez, O. et al. (Nahrung/Food 48(3) (2004)165-168) describe the preparation of milk protein from acid-precipitated casein by simultaneous transglutaminase and glucono-delta-lactone treatment. In publication J Agric Food Chem 52 (2004) 4456-4464, (Eissa, A. S., et al.), whey protein is treated at a low pH with a transglutaminase enzyme, and in publication J Dairy Sci 86 (2003) 1556-1563 (Vasbinder, A. J., at al.), solutions made from skimmed milk powder and whey protein-free milk powder were treated with transglutaminase and GDL or D-gluconic acid.
In said publications, the described processes and the raw materials used in them are, however, not industrially applicable but only suitable for research use.
Patent publication FI 20055076 (Valio Oy) describes a low-energy skimmed milk beverage rich in added calcium and containing a low-energy milk base of skimmed milk or whey protein solution or a combination thereof and from which carbohydrates have been removed either entirely or partly, and a process for preparing the same. The energy content of the product is at most 20 kcal/100 g.
Publication WO 2009/016257 relates to a process for producing an acidified milk drink and publication WO 2007060288, in turn, relates to a method of manufacturing soured dairy products. The protein contents of the raw materials used in these processes are in the range of about 30 w-% to about 42 w-% of the dry matter.
Today, retail and consumers require products that contain less energy and are structurally pleasing. It is thus desirable to provide and develop natural processes which are more efficient than before and which ensure the consumer-pleasing organoleptic properties of extremely low-energy products and the preservation of the structure of the product during transportation and even long-term storage.
It has now unexpectedly been found that it is possible to produce from a milk protein raw material having a standardized protein, fat and carbohydrate content extremely low-energy, either unsoured, that is, neutral, or soured milk products that are flawless and/or excellent in structure and taste without any additional costs.